Amorphization of crystalline Si due to heavy and light ion irradiation

Abstract

The formation of amorphous silicon in crystalline silicon by bombardment with light ͑Si͒ and heavy ͑Xe͒ ions has been investigated by transmission electron microscopy with in situ ion irradiation. Experiments have been carried out at room temperature and low temperature ͑50 K͒ and the results are compared to a simple numerical model for amorphization. The results indicate that the amorphization mechanisms for both irradiations are heterogeneous in nature and that numerous overlaps of the collision cascade are generally required to render the crystal amorphous. Following from this, the nature of the material within the confines of collision cascades will be discussed and it will be shown that the individual cascade volume is not necessarily amorphous as previously described in the scientific literature but contains varying degrees of damage depending on the energy deposited within the cascade.

An in situ transmission electron microscopy study of the ion irradiation induced amorphisation of silicon by He and Xe

“…It had previously been assumed that within the confines of a collision cascade the material is always rendered amorphous thus producing spatially isolated amorphous zones [9][10][11]. Recent work on the annealing of damage created by individual collision cascades [9,12], cascade overlaps [2] and cluster/molecular ion irradiation [13,14] has indicated that this may not necessarily be true with the cascade volumes consisting of variable levels of damage ranging from dilute up to completely amorphous.…”

“…Observations from Figure 1 indicate that in both irradiations, the amorphisation proceeds via a heterogeneous nucleation process rather than the homogeneous process that is generally accepted for low mass ions such as He [2]. However, a greater fluence by four-orders of magnitude (and over two-orders of magnitude greater in dpa) is required to achieve complete amorphisation in the case of He relative to Xe.…”

“…Many models for the amorphisation of materials under ion irradiation exist (see, for example, references [1][2][3]) and it is assumed that there are two basic mechanisms: heterogeneous and homogeneous. Generally, the homogeneous mechanism is assumed to be dominant during light ion irradiation and the heterogeneous mechanism during heavy ion irradiation [1][2][3].…”

“…Generally, the homogeneous mechanism is assumed to be dominant during light ion irradiation and the heterogeneous mechanism during heavy ion irradiation [1][2][3].…”

“…When the <220> spots were too faint to locate, line scans were taken from the locations relative to the 000 central spot at which the spots had last been observed. After background removal, the intensities in the amorphous halos were then measured and converted to an amorphous-ring intensity normalised to the fully-amorphous ring intensity [1,2].…”